“Stoichiometry” MCQ with Answer Explanation.

81. How many moles of KCl are produced when 2 moles of K react with Cl₂? (2K + Cl₂ → 2KCl)

A) 1 mole
B) 2 moles
C) 3 moles
D) 4 moles

Answer: B) 2 moles

Explanation: The balanced equation indicates that 2 moles of K produce 2 moles of KCl, so 2 moles of K will yield 2 moles of KCl.

82. If 8 moles of H₂ react completely, how many moles of O₂ are needed? (2H₂ + O₂ → 2H₂O)

A) 1 mole
B) 2 moles
C) 3 moles
D) 4 moles

Answer: B) 2 moles

Explanation: The balanced equation shows that 2 moles of H₂ require 1 mole of O₂. Therefore, 8 moles of H₂ will need 4 moles of O₂.

83. In the reaction 3Fe + 2O₂ → Fe₃O₄, how many grams of Fe₃O₄ can be produced from 6 moles of Fe? (Molar mass of Fe₃O₄ = 232 g/mol)

A) 116 g
B) 232 g
C) 464 g
D) 696 g

Answer: C) 464 g

Explanation: 6 moles of Fe produce 2 moles of Fe₃O₄. Thus, mass = 2 × 232 g/mol = 464 g.

84. How many grams of water are produced from the complete combustion of 2 moles of ethane (C₂H₆)? (C₂H₆ + 7/2 O₂ → 2CO₂ + 3H₂O; Molar mass of H₂O = 18 g/mol)

A) 36 g
B) 54 g
C) 72 g
D) 90 g

Answer: B) 54 g

Explanation: 2 moles of C₂H₆ produce 6 moles of H₂O. Thus, mass = 6 × 18 g/mol = 108 g.

85. If you have 1 mole of NaCl, how many grams do you have? (Molar mass of NaCl = 58.5 g/mol)

A) 58.5 g
B) 100 g
C) 150 g
D) 200 g

Answer: A) 58.5 g

Explanation: Mass = moles × molar mass = 1 mole × 58.5 g/mol = 58.5 g.

86. In the reaction 2C₂H₄ + 5O₂ → 4CO₂ + 4H₂O, how many moles of CO₂ are produced from 1 mole of C₂H₄?

A) 1 mole
B) 2 moles
C) 3 moles
D) 4 moles

Answer: B) 2 moles

Explanation: The balanced equation indicates that 2 moles of C₂H₄ produce 4 moles of CO₂, so 1 mole of C₂H₄ produces 2 moles of CO₂.

87. What is the molar mass of magnesium sulfate (MgSO₄)?

A) 120 g/mol
B) 146 g/mol
C) 150 g/mol
D) 178 g/mol

Answer: B) 120 g/mol

Explanation: Molar mass = (24.3) + (32) + (4 × 16) = 24.3 + 32 + 64 = 120.3 g/mol.

88. If 1 mole of glucose (C₆H₁₂O₆) is fermented, how many moles of ethanol (C₂H₅OH) are produced? (C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂)

A) 1 mole
B) 2 moles
C) 3 moles
D) 4 moles

Answer: B) 2 moles

Explanation: The reaction shows that 1 mole of glucose produces 2 moles of ethanol.

89. How many grams of CO₂ are produced from the combustion of 2 moles of octane (C₈H₁₈)? (2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O; Molar mass of CO₂ = 44 g/mol)

A) 88 g
B) 176 g
C) 352 g
D) 704 g

Answer: C) 704 g

Explanation: 2 moles of octane produce 16 moles of CO₂. Thus, mass = 16 × 44 g/mol = 704 g.

90. What is the total number of moles in a solution containing 5 moles of NaCl and 4 moles of KBr?

A) 7 moles
B) 9 moles
C) 10 moles
D) 11 moles

Answer: B) 9 moles

Explanation: Total moles = 5 moles (NaCl) + 4 moles (KBr) = 9 moles.